Hi Wachara, I have still not got a 3D printer.... I keep thinking about it, but always convince myself CNC can do it better. Although there are often certain shapes and small objects,.. clips etc where a 3D printer would certainly help. P.S. I like the Velcro strapping, what a brilliant idea. Hi ts8051, How did you measure the resonant frequency? 80Hz seems a bit low. Either you have a very large panel or low tension membrane? David.